Aerosol particles occur in the air we inhale and may have an adverse effect on the human health. In addition, inhalers produce different kinds of aerosol particles of different sizes, including nanoparticles where not only the presence but also the size distribution of the aerosol particles is an object of the interest. Furthermore, the detection of the aerosol particles and characteristics, such as their generation and the size, is essential in climate study and monitoring exhaust gasses and implementation of emission standards.
One barrier to the detection of aerosol particles having a diameter of less than the wave length of light is that they cannot be detected optically. A number of techniques exists for detecting aerosol particles having a size smaller than optically detectable, such as first charging the aerosol particle. The charged particles are collected and the induced electric current is measured in order to detect the presence or amount of the particles. Also, some detection techniques involve growing the aerosol particles by condensing a certain condensing fluid vapour on the aerosol particles before attempting detection.
The known methods have a number of drawbacks. Specifically, charging the particles before detecting makes the detecting device more complicated. Also, the charging may change the structure of the particles, such as the size of the particles and even decompose them (especially the smallest ones). In addition, the charging may produce particles whose size may match the size of the particles to be detected and thereby disturbing the actual measurement. In the charging method, the charging probability must also be known for particles of different sizes in order to detect the total numbers of particles. The charging probability is, however, very difficult to determine for the smallest particles.
In addition, the size or size distribution of the nanoscale aerosol particles cannot be detected but the known method relates mainly to particle counting or to indicating the presence of the aerosol particles.